Definition
Latin legal phrase meaning "at his own risk." The phrase operates as an allocator of legal risk, signifying that a person who acts in a particular capacity or undertakes a particular course of conduct does so bearing full personal responsibility for any resulting loss or harm. Where a legal rule places an obligation or permission sub suo periculo, the actor cannot shift adverse consequences onto another party — the risk rides with the actor.
Why It Matters in Research
This phrase is a compact risk-allocation formula that appears most frequently in medieval and early modern legal Latin sources. Researchers encountering it in translated treatises, plea rolls, or older equity opinions should treat it as a doctrinal signal, not mere rhetorical flourish: it typically marks the point at which a court or text is establishing who bears the burden if something goes wrong.
The phrase's natural habitat in the corpus is treatise law — particularly sources drawing on or influenced by Fleta and Bracton — rather than modern case law. A researcher tracing the phrase through Black's, Bouvier's, and Burrill's will find the definition stable and identical across all three, which is itself informative: this is a fixed maxim, not a term whose meaning evolved through common law adjudication.
Modern legal writing has largely displaced the Latin with English equivalents — "at his peril," "at his own risk," "at the risk of the actor" — but the underlying doctrine survived fully. When researching assumption of risk, strict liability precursors, or the allocation of loss in bailment and agency contexts, sub suo periculo and its English translations are effectively interchangeable in historical sources. Be alert to this when searching: limiting a corpus search to the Latin phrase will miss the majority of functionally identical doctrine expressed in English.
Historical Dictionary Support
All three shelf sources agree entirely on the definition ("at his own risk") and all three cite the same authority: Fleta, lib. 2, c. 5, § 5. The unanimity and identical citation suggest these entries descend from a common line of lexicographic transmission rather than independent research. Burrill adds the explicit label "L. Lat." (Law Latin), confirming this is a term of art native to the legal Latin tradition rather than classical Latin prose.
What the historical dictionaries do not provide is any elaboration of the legal consequences that flow from the designation. They define the phrase but leave the reader to infer its doctrinal work from context. Researchers should not expect these entries to distinguish between, for example, the phrase's use in property law (where a grantor or lessee acts at peril of title defect) versus its use in agency or procedure. That contextual specificity must be recovered from the surrounding text of the primary source.